PHASE DIAGRAM
DATE : 3 / 11 / 2015
PART A :
Determination of Phase Diagram of Toluene/ Ethanol / Water System Theory
OBJECTIVES :
- Determination
of the solubility limits in a ternary system of water and two other
liquids (ethanol and toluene), one of which is completely miscible
(ethanol) and the other is partly miscible with water (toluene).
- Construction of
the solubility curve of the system being studied on triangular diagram.
INTRODUCTION :
Phase diagram is a graphical
representation of the physical states of a substance under different conditions
of temperature and pressure . Ternary phase diagram are 3 components system .
For three-component system at constant temperature and pressure , the
composition may be stated in the form of coordinated for a triangular diagram .
In the diagram shown , each corner of the triangular diagram
represent a pure component which is 100% ( A, B , C ) . Mean while ,each
side represent two-component mixture and within triangular diagram itself
represent ternary components . Any line parallel to side of the triangular
diagram shows constant percentage value for a component , for example DE shows
20% of A varying amounts of B and C . So , does line FG , showing all mixture
containing 50% of B . These lines intercept with each other at K , which
definitely contain 20% A , 50% B as well as 30% C . Measurement can be made
this way because in a triangular diagram , the sum of all distance from K which
is drawn parallel to the three sides of diagram is same and equal to length of
any one side of the triangular diagram .
The addition of third component to a pair of miscible liquids can
change their mutual solubility . If this third component is more soluble in one
of the two different components of mutual solubility of the liquid pair is
decreased .However , when ethanol is added to a mixture of benzene and water ,
the mutual solubility is increased . Thus , when ethanol is added to a mixture
of benzene and water , the mutual solubility of the liquid pair increased until
it reached a point whereby the mixture become homogenous .
The benefits of preparing an oily substance as homogenous water in
liquid are already clear .
However what will happen to a system
like this when it is diluted should also be known as and this can be explained
through the understanding of triangular phase diagram . Figure 1 is also for
the system containing components peppermint oilpolysorbate 20-water . A
concentration of 7.5% oil , 42.5 % polysorbate20 and 50% of water ( point A in
diagram ) can be diluted for 10 times with the water giving a solution that is
still clear ( now containing 0.75 % of oil , 4.25% polysorbate 20 and 95% water
) .
However , when 1 ml of water is added to 10 ml of clear solution B ( 49%
oil , 5% polysorbate 20 and 1% water ) the solution become cloudy , point B’ (
44.5% oil , 45.45 % polysorbate 20 and 10% water ). If 1 ml of water is further
added , the solution become clear , point B’’ ( 40.5% oil , 41.3% polysorbate
20 , 18.2% water ) but if the original solution is diluted 3 times
( 16 1/3 % water , 16 2/3% polysorbate
20 and 67% water ) the solution become cloudy .
APPARATUS :
8 Conical Flasks
Burette
MATERIALS :
Toluene
Distilled Water
Ethanol
 |
| swirl the mixture until cloudiness formed |
1.Mixture of ethanol and toluene was
prepared in sealed container measuring 20 cm3 of the following
percentage ethanol in percent : 10 , 25 , 35 , 50 , 65 , 75 , 90 and 95%
.
2. 20 ml of each mixture is
prepared by filling a certain volume using a burette accurately .
3. A burette was filled with
distilled water .
4. Each mixture is titrated with
water until cloudiness is observed due to existence of a second phase .
5. The volume of distilled water
used was recorded .
6.Step 1 -5 were repeated for a second
titration . The volume of water required for complete titration of each mixture
was recorded .
7.Average volume of water used was
recorded .
8. The percentage based on the
volume of each component when the second phases start to separate was
calculated .
9. The points were plotted onto a
triangular paper with triangular axis to give a triple phase diagram.
RESULT
Percentage of Ethanol (%)
|
Volume of ethanol (mL)
|
Volume of toluene (mL)
|
Volume of water titrated (mL)
|
Average volume of water (mL)
|
|
Titration I
|
Titration II
|
||||
10
|
2
|
18
|
0.6
|
0.4
|
0.50
|
25
|
5
|
15
|
1.1
|
0.9
|
1.00
|
35
|
7
|
13
|
1.7
|
1.9
|
1.80
|
50
|
10
|
10
|
2.9
|
2.8
|
2.85
|
65
|
13
|
7
|
3.3
|
3.3
|
3.30
|
75
|
15
|
5
|
5.0
|
5.1
|
5.05
|
90
|
18
|
2
|
11.7
|
11.0
|
11.35
|
Percentage of Ethanol (%)
|
Ethanol
|
Toluene
|
Water
|
Total volume
|
|||
Volume (mL)
|
Percentage (%)
|
Volume (mL)
|
Percentage (%)
|
Volume (mL)
|
Percentage (%)
|
||
10
|
2
|
9.76
|
18
|
87.80
|
0.50
|
2.40
|
20.50
|
25
|
5
|
23.81
|
15
|
71.43
|
1.00
|
4.76
|
21.00
|
35
|
7
|
32.11
|
13
|
59.63
|
1.80
|
8.26
|
21.80
|
50
|
10
|
43.76
|
10
|
43.76
|
2.85
|
12.47
|
22.85
|
65
|
13
|
55.79
|
7
|
30.04
|
3.30
|
14.16
|
23.30
|
75
|
15
|
59.88
|
5
|
19.96
|
5.05
|
20.16
|
25.05
|
90
|
18
|
57.42
|
2
|
6.38
|
11.35
|
36.20
|
31.35
|
DISCUSSION:
In this experiment , A represents
ethanol, B represents toluene and C represents water. On each side of the
triangle, directly opposite the apex represents 0% of the apex component. 100%
of the component is represents by each apex of the triangle. Three lines
joining at the corner represent the component mixture of possible combination
of A and B, B and C, C and A respectively.
The system has only one phase but 3
component which in this experiment, the components are ethanol, toluene, and
water. According to Gibbs phase rule,
F = C – P + 2
where, F = number of degrees of freedom
in the system
P = number of phases present
In this experiment , the number of
degrees of freedom in the system is ;
F = C – P + 2
F = 3 – 1 + 2
F = 4
The 4 degrees of freedom in this
experiment including temperature, pressure, and concentration 2 out of 3
component. The third component concentration can be obtained by
calculation. Throughout the experiment, the temperature which is measured
to be at 26˚C and the pressure are kept constant. This will decrease the degree
of freedom to 2 and allow us to use a planar diagram to illustrate the
phase equilibria.
The experiment is first carried by preparing solution containing 10% ethanol and 90% toluene. At this point, the two components is miscible and exists in one phase. An average of 0.5 mL of water is added until cloudiness is observed which indicated that the second phase is formed. The percentage of the components is changed to 9.76% ethanol, 87.8 % toluene, 2.4% water. The experiment is repeated by increasing the percentage of ethanol to 25%,35%,50%,65%,75%,90% and the average volume of water for the second phase to appear is also increasing. This is because toluene and water are immiscible. thus, the higher the percentage of ethanol, will increased the mutual solubility ,more water is needed for second phase to occur.
From the data obtained, graph was
plotted inside a triangular diagram forming a binomial curve. Bounded region by
the binomial curve representing the two liquid phase so the mixture is cloudy.
Phase separation is indicated by the cloudy solution. Cloudy solution is formed
because there is not enough ethanol to produce homogenous mixture. High amount
of ethanol will act as surfactant allowing the two liquid phases become single
liquid phase. Regionabove the curve shows single liquid phase.
Few errors occur when doing this
experiment. One of the error that has affect percentage by volume and binomial
curve is degree of cloudiness of the liquid. No specific range of cloudiness is
fixed in each experiment causing the volume of water added to the solution
affected. This error can be overcome by fixing the degree of cloudiness in each
experiment. Ethanol and toluene are volatile liquid. It vapourise quickly
causing the actual volume of toluene and ethanol used in this experiment
is less than the measured. To avoid this from happening, we must quickly
titrate the toluene and ethanol after transferring it in the conical flask.
CONCLUSION:
Three-component system is important in
preparing the formulation of solution. The three components of ethanol,
toluene, and water in this system which is in one phase gives the degree of
freedom value of 4. However, the degree of freedom is reduced to 2 as the
temperature and pressure is kept constant. From the data, the higher the
percentage of ethanol, the higher the volume of water needed for the second
phase to appear. This is because toluene and water are immiscible. thus, the
higher the percentage of ethanol, will increased the mutual solubility ,more
water is needed for second phase to occur. Ternary phase diagrams represent the
phase behaviour of mixtures containing three components in a triangular
diagram. The ternary phase diagram is plotted and a binomial curve is obtained.
REFERENCES :
- Martin's
Physical Pharmacy and Pharmaceutical Science, Sixth Edition, Patrick J.
Sinko, Wolters Kluwer, Lippincott Williams & Wilkins.
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